A compound of formula I or a physiologically acceptable salt thereof ##STR1## wherein X represents sulphur or methylene, R.sub.1 represents hydrogen, amino or an acylated or carbamylated amino group, R.sub.2 represents hydrogen or an alkyl group and R.sub.3 represents an alkoxy group.
式I的化合物或其生理上可接受的盐##STR1##其中X代表
硫或亚甲基,R.sub.1代表氢、
氨基或酰化或
氨基甲酰化基团,R.sub.2代表氢或烷基,R.sub.3代表烷氧基。